HARRISBURG — Labor unions are widening their fight over legislation in Pennsylvania that aims to prevent the state and local governments from deducting union dues and union political action committee contributions from the paychecks of unionized workers. A raucous union rally today packed the Capitol Rotunda so tightly that police forced many more union demonstrators to wait outside in freezing cold. Members of private- and public-sector unions showed up to assail the legislation as an “attack on workers’ rights” led by out-of-state billionaires and conservative groups that don’t disclose their donors. No vote on identical House and Senate bills has been scheduled in the Republican-controlled Legislature. Democrats are opposed to it. Republican Gov. Tom Corbett says he’d sign it, while top House and Senate Republicans have been noncommittal.